[PATCH v2 2/2] mm: speed up mremap by 500x on large regions

Daniel Colascione dancol at google.com
Fri Oct 12 18:39:45 PDT 2018


Not 32-bit ARM?

On Fri, Oct 12, 2018 at 6:35 PM, Joel Fernandes <joel at joelfernandes.org> wrote:
> On Fri, Oct 12, 2018 at 11:18:36AM -0700, David Miller wrote:
>> From: Joel Fernandes <joel at joelfernandes.org>
> [...]
>> > Also, do we not flush the caches from any path when we munmap
>> > address space?  We do call do_munmap on the old mapping from mremap
>> > after moving to the new one.
>>
>> Sparc makes sure that shared mapping have consistent colors.  Therefore
>> all that's left are private mappings and those will be initialized by
>> block stores to clear the page out or similar.
>>
>> Also, when creating new mappings, we flush the D-cache when necessary
>> in update_mmu_cache().
>>
>> We also maintain a bit in the page struct to track when a page which
>> was potentially written to on one cpu ends up mapped into another
>> address space and flush as necessary.
>>
>> The cache is write-through, which simplifies the preconditions we have
>> to maintain.
>
> Makes sense, thanks. For the moment I sent patches to enable this on arm64
> and x86. We can enable it on sparc as well at a later time as it sounds it
> could be a safe optimization to apply to that architecture as well.
>
> thanks,
>
>  - Joel
>



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